<!doctype html>
<head>
<script>
function start() {
  var animation = document.body.animate([{marks: 'crop'},{marks: 'crop'}], 12);
  document.write('<html><body></body></html>');

  setTimeout(function() { animation.play(); }, 4);
  setTimeout(function() {
    animation.timeline = undefined;
    SpecialPowers.Cu.forceGC();
    window.top.continueTest();
  }, 5);
}
</script>
</head>
<body onload="start()"></body>
</html>

